Field of the Invention
The present invention relates to a fuel cell formed by stacking a membrane electrode assembly and a separator. The membrane electrode assembly includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. Further, the present invention relates to a method of operating the fuel cell.
Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a solid polymer ion exchange membrane. In the fuel cell, the solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). Each of the anode and the cathode includes electrode catalyst as an electrode catalyst layer and porous carbon as a gas diffusion layer. The membrane electrode assembly is sandwiched between separators (bipolar plates) to form a power generation cell. In use of the fuel cell, generally, a predetermined number of power generation cells are stacked together to form a fuel cell stack, e.g., mounted in a vehicle.
In this type of fuel cell, in some cases, a fuel gas permeates from the anode side to the cathode side through the solid polymer electrolyte membrane, and an oxygen-containing gas permeates from the cathode side to the anode side through the solid polymer electrolyte membrane.
In the structure, at the anode and the cathode, hydrogen peroxide (H2O2) tends to be generated easily (H2+O2→H2O2) by the reaction of hydrogen and oxygen. This hydrogen peroxide is decomposed on carbon carriers and platinum (Pt) in an electrode, and for example, active substances such as hydroxyl radical (.OH) are generated. As a result, the solid polymer electrolyte membrane and the electrode catalyst are degraded disadvantageously.
In this regard, a system of operating a fuel cell disclosed in Japanese Patent No. 4554163 (hereinafter referred to as the conventional technique) is known. This conventional technique relates to a system of operating a fuel cell formed by stacking a plurality of electrode assemblies through separators. Each of the electrode assemblies includes a fuel electrode, an oxygen electrode, and an electrolyte interposed between the fuel electrode and the oxygen electrode. A fuel gas containing hydrogen is supplied to the fuel electrode, and an oxygen-containing gas is supplied to the oxygen electrode.
The operating system includes hydrogen peroxide concentration measurement means for measuring concentration of hydrogen peroxide contained in at least one of a fuel electrode side exhaust gas and a fuel electrode side collected water discharged from the fuel electrode and an oxygen electrode side exhaust gas and an oxygen electrode side collected water discharged from the oxygen electrode, determining means for determining whether or not the hydrogen peroxide concentration measured by the hydrogen peroxide concentration measurement means is a predetermined upper limit value or less, operating condition control means for controlling at least one of current density, pressure of the fuel gas, gas excess ratio at the fuel electrode, gas excess ratio at the oxygen electrode, relative humidity of the fuel gas, and relative humidity of the oxygen-containing gas as operating conditions of the fuel cell, if it is determined that the hydrogen peroxide concentration exceeds the upper limit value, so as to suppress generation of hydrogen peroxide.
According to the disclosure, in the structure, it is possible to keep track of the state of generation of hydrogen peroxide as a cause of degradation in the cell performance, and by controlling the operating conditions as necessary, it becomes possible to stably operate the fuel cell over a long period of time without suffering degradation in the cell performance.